1. Field of the Invention
The present invention relates to a coated tool provided with a wear-resistant coating film on its surface, and more particularly, it relates to a coated cutting tool employed for milling, turning, drilling and the like, and a coated tool such as a coated mold, punch and die employed for metal forging, punching, pressing and the like.
2. Description of the Background Art
In recent years, new tool materials have been developed one after another, in order to satisfy a requirement for higher efficiency and higher precision of working. In the process of such material development, techniques of coating various tool materials with ceramics for manufacturing the so-called coated tools are indispensable. As a recent trend, working speeds are now increasing, in order to improve working efficiency. As a result, ceramics coating films provided on surfaces of such tools become remarkably worn.
In order to suppress such wear, titanium ceramics such as titanium carbide (TiC), titanium nitride (TiN) or titanium carbo-nitride (Ti(C,N)) are most generally employed as a component of a ceramics coating film for a cutting tool, for example. Further, there has been developed a method of improving wear resistance and oxidation resistance of such a ceramics coating film by adding aluminum into the titanium ceramics material. Thus, titanium aluminum nitride ((Ti,Al)N) is now coming into wide use as the material for a ceramics coating film.
When such a coating film is formed on a coated cutting tool, however, the material being cut (hereinafter referred to as a workpiece) is disadvantageously deposited onto the ceramics coating film around the insert of the tool to induce chipping, the so-called deposition chipping, of the insert. Such deposition chipping takes place conceivably because the adhesion force between the ceramics coating film serving as a wear-resistant coating and the deposit is so high that the deposit grows on the cutting edge to cause a phenomenon such as remarkable chipping on the forward end portion of the insert.
In perforation work using a drill provided with a ceramics coating film, on the other hand, effusion resistance of swarfs is increased to break the drill particularly in case of drilling a deep hole.
In order to solve these problems, a tool prepared by depositing a lubricative coating consisting of a layer compound such as molybdenum disulfide on a wear-resistant coating film has been proposed and put on the market. In such a tool, the layer compound such as molybdenum disulfide is easily worn due to low mechanical strength. Immediately after starting of cutting, therefore, the problem such as deposition chipping or increased effusion resistance is hardly caused, due to the lubricative action of molybdenum disulfide. However, the quantity of molybdenum disulfide is reduced with progress of cutting, to readily cause the problem of deposition chipping or increase of effusion resistance of swarfs.
In order to suppress such deposition chipping or increase of effusion resistance of swarfs, therefore, a large quantity of cutting fluid is generally employed during cutting. However, such employment of the cutting fluid leads to an environmental problem. In case of working a deep hole with a drill, further, it is difficult to feed such a cutting fluid to the forward end portion of its insert. Thus, a tool which can withstand high-speed cutting with no cutting fluid is needed.
Also in relation to a mold, a technique of coating its base material with ceramics is indispensable. As the recent trend, further, warm or hot forging is now coming into use, in order to implement improvement of working accuracy or reduction of a lubricant coating step. Thus, wear of the mold material is remarkable.
In order to suppress such wear, the ceramics coating film for the mold is prepared from a component similar to that for the cutting tool. However, such a ceramics coating film is inferior in lubricity, although the same is effective for improving wear resistance. Therefore, a technique of forming a bonderizing film on the workpiece or using lubricating oil, graphite or a boric acid lubricant during working is employed.
The term "bonderizing" indicates formation of a zinc phosphate coating film on the surface of a workpiece. Thus, it is possible to suppress the so-called galling of the workpiece and the mold material during cold forging. However, the surface of the mold material must be cleaned with acid in a pretreatment for the bonderizing, disadvantageously leading to a large quantity of waste solution. Further, the cold-forged workpiece is hardened, and must be annealed after the cold forging. The zinc phosphate coating film separates from the surface of the workpiece at this time, and hence the workpiece must be bonderized again after the annealing.
In order to solve these problems in cold forging, warm or hot forging is widely employed. Flow stress of the workpiece can be reduced by increasing its temperature (to at least 500.degree. C. in forging of a ferrous material, for example), thereby reducing a mechanical stress load on the mold. Further, the workpiece does not need to be annealed/bonderized after forging.
In the warm or hot forging process, however, no reliable lubrication method can substitute for bonderizing. Although a method using a solid lubricant of graphite or boric acid is employed, sufficient lubricity is not attained, so that the surface of the mold is remarkably worn in this method. Thus, a mold which is hardly worn in cold, warm or hot forging is needed.